WASHINGTON — The Obama administration said Saturday it had reduced the error rate in enrollment data sent to insurance companies under the new health care law, even as insurers said that files they had received from the government in the past few days were riddled with mistakes.

The quality of the data is important; it could affect the ability of people to get medical care and prescription drugs when they go to doctors’ offices and pharmacies starting next month.

More than 137,000 people selected health plans in the federal insurance marketplace in October and November, and administration officials say that more than 100,000 signed up in the first week of this month.

For each person who signs up, the government is supposed to send information electronically to an insurance company in a standard format known as an 834 enrollment transaction. In some cases, consumers selected a health plan at the federal website, Healthcare.gov, but the government did not notify the insurance company.

In other cases, insurers received duplicate files for the same person, files for one person were sent to an insurer in another state, or the “relationship code” was wrong so that, for example, a man’s daughter was listed as his wife.

The White House said Saturday that the government was now informing insurance companies of nearly all new enrollments.

“Between Oct. 1 and Dec. 5, the number of consumers for whom 834s were not produced was fewer than 15,000,” said Julie Bataille, a spokeswoman at the federal Centers for Medicare and Medicaid Services. “Since the beginning of December, missing 834s as a percentage of total enrollments has been close to zero.”

Bataille said most of the problems had occurred from Oct. 1 to mid-November, as enrollment reports on some consumers “were either not being generated, or had errors due to larger technical system issues.”

On Tuesday and Wednesday, the government sent information to insurers listing everyone who had enrolled in a health plan through the federal marketplace. Insurers are supposed to compare the information with their own records and with the daily reports they have received from the government over the past 10 weeks.

Insurers said that they had found many discrepancies and errors and that the government was overstating the improvements in Healthcare.gov.

In some cases, they said, the federal government reported that the home address for a new policyholder was outside an insurer’s service area. In other cases, a child was listed as the main subscriber — the person responsible for paying premiums — and parents were listed as dependents.

In some cases, children were enrolled in a policy by the federal government and parents were left off, or vice versa. In other cases, the government botched up the members of a family: A child or spouse was listed two or three times in the same application in late November. Such errors can have financial implications, increasing the amount of premiums that a family is required to pay.

While some of the problems were discovered in the past few days, insurers said that they had previously reported many of the errors to the “help desk” at the Centers for Medicare and Medicaid Services, and that the problems remained unresolved.

Federal officials, insurers and health care providers said they were concerned about confusion and possible chaos in the early days of January, when people try to use the new insurance coverage they believe they have.

The government’s overriding message to insurers is: Do whatever you have to do to maximize enrollment and to provide coverage by Jan. 1 to anyone who wants it. Federal health officials have told insurers that they can sort out the details and work out financial arrangements with the government later.

People have until Dec. 23 to sign up for coverage that begins in January, and they have until Dec. 31 to pay premiums for the first month. But the administration has encouraged insurers to relax those deadlines and to take other steps to ensure a smooth transition for people joining their health plans.

Some of the new enrollees have never had insurance. Others turned to the federal exchange because their current insurance policies were being canceled or discontinued on the ground that they do not comply with coverage requirements of the new health care law.